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Astronomers discover sandstorms in space
Astronomers at The University of Manchester believe they have found the answer to
the mystery of a powerful ‘superwind’ which causes the death of stars.
Writing in Nature, the team of researchers, lead by Barnaby Norris from the
University of Sydney in Australia, used new techniques which allowed them to look
into the atmospheres of distant, dying stars.
The team includes scientists from the Universities of Manchester, Sydney, ParisDiderot, Oxford and Macquarie University, New South Wales. They used the Very
Large Telescope in Chile, operated by the European Southern Observatory.
At the resolution used by the scientists, one could, from the UK, distinguish the two
headlights on a car in Australia. This extreme resolution made it possible to resolve
the red giant stars, and to see the shells ejected by their winds.
Stars like the Sun end their lives with a ‘superwind’, 100 million times stronger than
the solar wind. This wind lasts over a period of 10,000 years, and removes as much
as half the mass of the star. At the end, only a dying and fading remnant of the star
will be left. The Sun will begin to throw out these gases in around five billion years.
The cause of this superwind has remained a mystery. Scientists have assumed that
they are driven by minute dust grains, which form in the atmosphere of the star and
absorb its light. The star light pushes the dust grains (silicates) away from the star.
However, models show that this mechanism does not work well. The dust grains
become too hot, and evaporate before they can be pushed out.
The scientists have now discovered that the grains grow to much larger sizes than
had previously been thought. The teams found sizes of almost a micrometer – as
small as dust, but huge for stellar winds.
Grains of this size behave like mirrors, and reflect starlight, rather than absorbing it.
This leaves the grains cool, and the star light can push them out without destroying
them. This may be the solution to the mystery of the superwind. The large
grains are driven out by the star light at speeds of 10 kilometer per second, or 20
thousand miles per hour – the speed of a rocket. The effect is similar to a
sandstorm. Matter of speaking of course – compared to grains of sands, the silicates
in the stellar winds are still tiny.
Professor Albert Zijlstra, from The University of Manchester’s Jodrell Bank
Observatory, sad the breakthrough changes our view of these superwinds. For the
first time, we begin to understand how the superwinds work, and how stars
(including, in the distant future, our Sun) die.
He added: “The dust and sand in the superwind will survive the star, and later
become part of the clouds in space from which new stars form. The sand grains at
that time become the building blocks of planets. Our own Earth has formed from star
dust. We are now a big step further in understanding this cycle of life and death.“
Notes for Editors:
The paper, A close halo of large grains around red giant stars: a new piece in the
mass-loss puzzle, by Barnaby Norris, Peter Tuthill, Michael Ireland, Sylvestre
Lacour, Albert Zijlstra, Foteini Lykou, Thomas Evans, Paul Stewart, and Timothy
Bedding, is available; on request from the Press Office.
Professor Zijlstra is available for interview on request
For media enquiries please contact:
Daniel Cochlin
Media Relations Officer
The University of Manchester
0161 275 8387
[email protected]